The stem/threaded length of the bleed valve is not that short, unless the corrosion is that bad but the component itself is stout for its size. I’ve never snapped one before but I did unintentionally rounded a few because of how bad the corrosion and how the previous person strong handed it that it was already close to round and stuck.
View attachment 4006636
The corrosion/rust on the brake hard lines is primarily from the chemistry composition of fluid. The lower DOT rating it has (glycol-based) the more susceptible it is to moisture hence oxidation = corrosion = rust. The higher the dot rating, the lower the chance for it to absorb moisture or even repel it (DOT5 silicone-based).